It was to have been a silent vigil outside the White House last night in solidarity with Cindy Sheehan, the Gold Star Mother-turned-antiwar activist. But the 500 demonstrators were not the sort to be silenced.

"Meet with Cindy!" they chanted. "Tell her the truth! . . . This war was for oil! . . . End the war now!"

"Cindy Sheehan," organizer Karen Bradley shouted into a megaphone, "you are an inspiration to us all!"

As Sheehan, mother of an American soldier killed in Iraq, camps out near President Bush's ranch in Texas this month in symbolic protest, foes of the war see the chance to achieve something that has eluded them for two years: galvanizing a mass antiwar movement. Sheehan, they say hopefully, could be their Rosa Parks.

Bradley, a volunteer for the liberal group MoveOn.org, which coordinated about 1,600 candlelight vigils across the country last night for Sheehan, certainly thinks so. "We've been missing this galvanizing, iconic figure," said Bradley, who lost a child nine years ago, to illness. "I think all the mothers of the world are going to come out and say, 'Enough.' "

That's what worries Kevin Pannell, whose knot of a dozen conservative counterdemonstrators was outnumbered 50 to 1 on Pennsylvania Avenue last night. Pannell, part of the Army's First Cavalry Division, lost both calves in Iraq last year when his patrol was ambushed in a grenade attack. He said he had never been to a political rally before, but he is worried about Sheehan's ability to spark an antiwar movement.

"She's stirred up a wasps' nest," he said, leaning on a flagpole to support his prosthetic legs. "It's definitely getting bigger. They're getting a little out of hand."

MoveOn.org is leaving nothing to chance as it tries to make Sheehan into a national icon. It supplied demonstrators with advice on media relations. ("When talking to reporters, it is OK to keep repeating the same message over and over. It may feel strange to do that, but the reporters are used to it.") MoveOn.org designed printable placards for participants proclaiming "Dogs for Cindy" and "Moms for Peace." It directed vigil hosts to declare "if you have pets your guests could be allergic to."

"We're also asking that you bring pictures of children," MoveOn.org requested, and it didn't matter "whether or not you have a child serving in the military."

"Every movement has a moment when it torques up," said Tom Matzzie, the group's Washington director. "Cindy is the Rosa Parks of the peace movement in 2005. Cindy, Rosa Parks, Paul Revere -- they're people who try to start something."

Sheehan will have to make her ride into immortality without the help of Longfellow. But is it possible this moment could make MoveOn.org what SDS (Students for a Democratic Society) was during Vietnam? "I'm only 30," Matzzie replied. "I don't really understand the reference that much."

Kristinn Taylor does. An organizer for FreeRepublic.com, a MoveOn.org counterpart on the right, he recruited a small group of conservatives to hold a counterprotest last night; they stood beneath the statue of Andrew Jackson and held a banner, stitched from three bedsheets, proclaiming: "God Bless Our Soldiers Liberating the World of One Tyrant at a Time."